INTERACTION BETWEEN TRYPTOPHAN RESIDUES AND HYDROPHOBICALLY-MODIFIED DEXTRAN - EFFECT ON PARTITIONING OF PEPTIDES AND PROTEINS IN AQUEOUS 2-PHASE SYSTEMS

Hydrophobically modified dextrans, benzoyl dextran and valeryl dextran , have been used to study the interactions between tryptophan residues and benzoyl or valeryl groups by partitioning of tryptophan, tryptoph an-tryptophan, (tryptophan),, poly(lysine, tryptophan), beta-galactosi dase and lysozyme in polymer aqueous two-phase systems. The two-phase systems used were polyethylene glycol (PEG)-benzoyl dextran, PEG-valer yl dextran, dextran-benzoyl dextran and dextran-valeryl dextran. Inter action between tryptophan residues and benzoyl or valeryl groups was o bserved by partitioning of tryptophan containing compounds to the phas e containing hydrophobically modified dextran. At a certain phase comp osition the interactions were increased with increasing number of tryp tophan per molecule. In a PEG-dextran system the partitioning of trypt ophan peptides to the PEG phase was increased with increased number of tryptophan. In a PEG-benzoyl dextran system the opposite effect was o btained. At similar conditions benzoyl groups showed stronger interact ions with tryptophans compared to valeryl groups. The partition coeffi cient of salts (sodium phosphate, NaCl, NaI and NaClO4) was determined in PEG-benzoyl dextran and PEG-valeryl dextran aqueous two-phase syst ems. The effect of addition of these salts on partitioning of poly(lys ine, tryptophan), beta-galactosidase and lysozyme was studied. Salt ef fects on partitioning could be explained by the relative affinities of the ions for the polymers in the system. Charged molecules containing tryptophan were to an increasing degree partitioned to the phase for which the counterions had highest affinity. Strong effects on the part itioning of positively charged poly(lysine, tryptophan) and lysozyme w ere obtained with the ions I- and ClO4-.